Parent GM GM.UL put loss-making Saab up for sale more than a year ago so it could focus on its own financial problems, but one deal collapsed and GM said it would end Saab production if a credible buyer could not be found by the start of this year.
Shares in Spyker have skyrocketed on speculation it was close to clinching a deal.
Negotiations are ongoing and the spirit is positive, but we are very, very tired, Spyker chief executive Victor Muller told Reuters while in Stockholm, where he is holding talks.
It is such a complicated transaction. It's not for no reason it has taken so long. It is extremely technical, he said. It can go either way, but you can rest assured we are doing everything to close the deal.
Spyker -- which made 43 luxury cars last year against Saab's sales of 93,295 -- has faced some skepticism from the start, given that the Dutch company has never made a profit.
A deal to sell Saab to tiny luxury car maker Koenigsegg fell through last November and GM said then it would start winding down Saab -- though it would consider offers in the meantime.
This sparked a frantic scramble to get new bids in, with Spyker heading the pack.
Analysts previously have been pessimistic about the chances of doing a deal. Some have questioned GM's willingness to sell technology that could compete with its own models.
Others have focused on the short timeframe for buyers to organize funding and prepare a business plan.
Spyker has had to update its bid several times and it remains unclear whether it has been able to meet all GM's demands.
It is now the sole bidder after investment company Genii Capital, backed by Formula One mogul Bernie Ecclestone, withdrew its offer on Monday.
Spyker shares were down 5.8 percent at 1138 GMT, but are up more than 70 percent since the start of the year.
Dutch financial authorities announced that trading in Spyker shares was suspended, without giving a reason, although this is sometimes done before a company announcement during trading hours.